Prusa error 13817 (Heaters Timeout) appears on the MK4 and its equivalents are #26817 on the MK4S and #21817 on the MK3.9. The printer waited for the hotend or heatbed to reach the target temperature but one of them failed to get there within the allowed time window, triggering a halt.

What the Error Means

The firmware sets a maximum time limit for the hotend and heatbed to reach their target temperatures. If the temperature is climbing too slowly — reaching, say, only 180°C when 215°C is needed, and stalling there — the printer concludes the heater or thermistor is not functioning correctly and halts. Cold ambient environments (rooms below 15°C) can genuinely slow heating enough to trigger the timeout on a healthy printer. More commonly, the cause is a partially disconnected heater cable that reduces power delivery, a heater cartridge that has partially failed and is now underperforming, or a thermistor that is reading high (making it seem like the temperature is not rising when it actually has).

Step-by-Step Fix

1. Check the ambient room temperature. Heating in very cold rooms — below 15°C — can slow the initial temperature rise enough to trigger the timeout even with healthy hardware. Move the printer to a warmer environment if possible.
2. Inspect the hotend heater cartridge wiring. Trace the heater cable from the nozzle assembly to the LoveBoard connector. Look for a loose, partially inserted connector, damaged insulation, or a cable that appears kinked near the nozzle. Reseat the connector if loose.
3. Check the heatbed cable connections. Verify that the heatbed power cable is firmly connected at the bed underside and at the xBuddy board. A loose bed cable significantly reduces heating power.
4. Run a preheat test from the menu. Navigate to LCD Menu → Preheat and select a preset for your filament. Watch whether both the hotend and bed temperature curves rise steadily. If one stalls far below target within 3–5 minutes at room temperature, that component has a heater fault.
5. Replace the heater cartridge or thermistor if one fails the preheat test. A heater cartridge that cannot sustain its rated wattage, or a thermistor that reads incorrectly and masks temperature progress, needs replacement.

Parts Required

• Replacement hotend heater cartridge (if hotend fails to heat to target temperature)
• Replacement hotend thermistor (if thermistor readings are suspect)
• Replacement heatbed cable (if bed cable shows damage or loose connection)
• Digital multimeter (to measure heater and thermistor resistance)

If both components heat correctly in isolation but the timeout still fires, contact Prusa Support at help.prusa3d.com for further diagnosis of the xBuddy board’s temperature monitoring logic.

Frequently asked questions

What does Prusa 13817 mean?

Prusa error 13817 (Heaters Timeout) appears on the MK4 and its equivalents are #26817 on the MK4S and #21817 on the MK3.9. The printer waited for the hotend or heatbed to reach the target temperature but one of them failed to get there within the allowed time window, triggering a halt.

How do I fix Prusa 13817?

Prusa error 13817 means the hotend or bed took too long to reach target temperature. Learn how to check heater cables, thermistors, and connections to restore heating.